Hydraulic fracturing processes (also referred to in the art as “fracking”) are used to break up reservoir rock. During fracking operations, a packer assembly having a one-way valve is often used to isolate reservoirs and/or production zones by sealing off lower zones in a borehole in order to carry out a hydraulic fracturing process on higher zones. Packer assemblies using such one-way valves are generally referred to as “frac plugs”. Often fracking operations will use multiple frac plugs so as to isolate several zones so as to carry out fracking of such zones in different stages.
A packer assembly provides a seal between the outside of the frac plug and inside of the casing so as to prevent fluid flow outside of tubing utilized in well operations. A packer assembly may allow for fluid flow through its mandrel and hence through the tubing to which it is connected. In a frac plug, the one-way valve provides for one-directional flow upward through the tubing by governing flow through the mandrel of the frac plug, which is in fluid flow communication with the tubing.
Frac plugs can utilize various valves to provide for one-way directional flow through the packer assembly, such as ball/ball seat assemblies and poppet valve assemblies. Where ball/ball seat assemblies are used, the Frac plug has two-way directional flow (upward and downward) prior to introduction of the ball. The ball can be introduced by dropping it downhole and subsequently introducing it to the ball seat by gravity and/or fluid pressure. In poppet valve assemblies, downward flow through the packer assembly can be initially provided by propping open the poppet valve. When downward flow is no longer desired, backflow (upward flow) through the poppet valve can be used to release the prop and, thus, activate the valve to prevent downward flow.
After the fracking operation, the frac plugs are then removed to allow fluid flow to or from the fractured rock. Some frac plugs are designed to be removed by lowering a tool downhole to disengage the frac plug and return it up hole; however, such removal is more costly and time consuming than other removal methods. More typically, frac pugs are made of drillable composites and/or metal and are removed by drilling them out of the borehole. In some cases, the frac plug elements have been formed of a material that reacts with the ambient downhole environment so that they need not be physically removed by the aforementioned mechanical operations, but may instead corrode or dissolve under downhole conditions. However, because operations such as fracking may not be undertaken for months after the borehole is drilled, such elements may have to be immersed in downhole fluids for extended periods of time (for example, up to a year, or longer) before the fracking operation begins. Therefore, use of dissolvable components can be problematic because the frac plug may become inoperable before fracking commences.